Method of and means for superheat control



Aug. 27, 1940. c DAVY 2,213,121

METHOD OF AND MEANS FOR SUPERHEAT CONTROL Filed Nov. 11, 1936 Eg'fl-4a INVENTOR.

hrmo aher H. Davy EE-QR ATTORNEY.

Patented Aug. 27, 1940 uNrrso srrss run METHOD'OF AND MEANS FOR SUPER- HEAT CONTROL Christopher Humphrey Davy, Blackheath, London, England, assignor to The Babcock & Willcox Company, Newark, N. 3., a corporation of New Jersey Application November 11, 19:36, Serial No. 119,232 In Great Eritain January 13, 1936 15 Claims.

, flow of the gases through the bypass in response with the control.

to variations of the superheat from a predeterminedvalue. I

Other examples of the application of the invention are the control of heating gases in heat exchangers and the control of gas or air flow in the ventilating shafts in buildingsor mines. The invention is not to be considered as limited thereto, but it is to be taken as of Wider application.

Iniaccordance with my improved method I control the flow of fluid through a conduit by projecting one or more secondary streams of fluid athigher pressure across the flow in the conduit, thereby reducing the effective area of the passage to the flow of the fluid: to be controlled. The secondary stream or streams of fluid may be taken from another source or from a point in the controlled flow located on the downflow side of the control point and sufficiently remote therefrom so as to present no undue interference The means for carrying the method into effect preferably comprises a blower or injector fan connected to one or more nozzles disposed in the walls of the conduit and adapted to deliver one ormore secondary streams of fluid at higher pressure transversely of the direction of flow cfthe fluid to be controlled.

Considering the application of the invention to a superheate-r in which a part of the furnace gases bypass the superheatcr, the control of the r. b-y-pass gases is effected by injecting or project- Fig. l is a view in the natureof avertical cross section of a steam generator fitted with my improved superheat controlling means;

Fig. 2 is a view in the nature of a vertcal cross section through another steam generator which is an additional embodiment of the invention.

Fig. 3 is a diagrammatic view on a much larger scale illustrating a general application of the invention.

In the embodiment of the invention indicated 10:

in Fig. l of the drawing thesteam generator consists of a lower bank of tubes land an upper bank of tubes all of which communicate at their ends with directly connected uptake and downtake headers. The circulatory system of the .5-.

boiler is completed by horizontal circulators 2' and a steam and water drum.

A superheater s is located in thespace between the tube banks i and 2 and the two uppermost rows of tubes i of the lower bank are bent so as to connect the upper end of the downtake header ii with the lower end of the uptake header ii of the upper bank of tubes 2. The intermediate portions of these'bent tubes are spaced as indicated so as to define a gas bypass 8 which is closed at its sides by battles or tiles l supported by the tubes t. This bypass conducts gases around the superheater and directly to the upper bank of tubes 2.

Nozzles project into the bypass 8 or are other- 80- pass and it is supplied to the nozzles through 35 the pipe it] by means of a fan or blower 55 connected to a suitable source by the pipe 5 i. This source may be at a point on the downstream side of the control point remote therefrom, or the pipe H may be connected with the discharge side 42 1$ of an induced draft fan ib drawing the gases of combustion through the breeching M from the steam generator.

The fluid or gaseous medium projected through the nozzles s acrossthe stream of gases flowing 5 through the bypass 8 serves to reduce the effective flow area of the stream and to increase the resistance to the flow-of the gases. By regulating the speed of the fan or blower M, or otherwise controlling the flow of gases to the blowerthe 5'0 flow of gases can be regulated and the now of combustion gases through the bypass thereby controlled. This effects a consequent control of superheat and'this control may be made automatic by the installation of conventional auto- 551,

matic control means 31 varying the flow of fluid projected across the bypass in response to departures of superheat from a predetermined value, or partly in response to such variations and partly in response to variations in steam flow from a predetermined value.

In the embodiment of my invention illustrated in Fig. 2 of the drawing the superheater or superheaters 13 may be located above a single bank of tubes I. The bypass I8 is defined by water circulating tubes l4 covered with baflle tile ii and extending from the downtake header construction l5 to the header 22 located above the superheater. The header 22 is connected to the steam and water drum 23 by means of tubes 24. Alternately, as shown in chain-dotted lines, the water circulating tubes M defining the bypass l8 may be connected with a header 25 which in turn is connected with the steam and water drum 23 by means of tubes 26.

Nozzles l9 project into the bypass l8 and are supplied with a fluid medium at a pressure higher than the pressure offluid passing through the bypass. This supply is effected by one or more pipes 20 connected with a fan or blower 2! the inlet of which communicates with any suitable source of fluid by means of the conduit 2i. By regulating the speed of the fan or by other means the quantity of combustion gases flowing through the bypass l8 can be controlled and the superheater thus regulated.

Apparatusforeffecting the illustrative method of fluid flow control is illustrated diagrammatically in Fig. 3. The flow of a fluid to be controlled takes place in the conduit 3| transversely of which a nozzle 32 projects through a wall of the conduit at a point at which the control is to be efiected. This nozzle is supplied with a fluid or a gaseous medium under a pressure higher than the pressure of the fluid tobe controlled. This supply is efi'ected by a fan 33. By regulating the fan or the supply of gaseous fluid to the fan a reduction in the effective flow area to the con duit is brought about. Thus superheat is controlled by the efi'ect of a high pressure blast across the conduit through which the controlled flow is taking place.

By way of automatic control means for the high pressure blast through the nozzles 32, Fig, 3 of the drawing shows a rheostat arm 33 actuated by an operator 3? which is connected to the bell crank 38. The operator is in turn controlled by the pressure of fluid in a line 44 communicating with a thermally responsive element 43. The latter is shown disposed in the header 35 which may be the outlet header for the superheater.

In Fig. 3 the fluid for the high pressure blast is supplied by a pipe 34 which may be fitted with suitable valves or dampers and connected at a remote point on the downstream side of the conduit or connected with some other suitable source such as the exhaust of a fan drawing the gaseous fluid through a conduit.

Whereas the invention has been described with reference to a number of specific embodiments it is to be understood that the invention is not limited thereto. It is rather, susceptible of use in different combinations within the scope of the sub-joined claims.

I claim:

1. A method of regulating the temperature of superheated steam passing from a superheater disposed in the main part of the flow of combustion gases and positioned adjacent a bypass through which a portion of the combustion gases normally passes around the superheater without contacting therewith, the method consisting in projecting across the bypass a stream of fluid at a pressure higher than that of the pressure of the gases passing through the bypass and thereby regulating the effective flow area through the bypass and consequently the flow of gases over the superheater.

2. In fluid heat exchange apparatus, means for conducting a fluid at one temperature in restricted streams across a part only of a stream of fluid at a difierent temperature, and high pressure blast means projecting a stream of fluid at higher pressure across the remainder of the flow of the second mentioned fluid to thereby control the rate of heat exchange between the fluid in the restricted streams and the other fluid, the different parts of the flow of the second mentioned fluid being separated in continuously open flow paths.

3. In a superheater, a group of spaced tubes conducting steam across a part of the flow of furnace gases, means providing a constantly open bypass at one side of the superheater, a part of the furnace gases normally flowing through the bypass, and high pressure blast means projecting a flow of higher pressure fluid into the bypass to maintain superheat at a predetermined value, the superheat being thereby regulated by control of gas flow without the use of dampers.

4. A method of controlling the temperature of superheated steam passing from a superheater disposed in the main flow of combustion gases and positioned adjacent a constantly open bypass which permits a portion of the combustion gases to pass around the superheater without contact therewith, the method consisting in projecting across the bypass a stream of fluid at a pressure higher than that of the pressure of the gases passing through the bypass and thereby controlling the effective flow area through the bypass and consequently the flow of gases over the superheater, and varying the flow of the projected higher pressure fluid in response to variations of the superheat from a predetermined value.

5. In fluid heat exchange apparatus, means for conducting a fluid at one temperature in restricted streams across a part only of a stream of fluid at a different temperature, means providing separate and constantly open passes for the parts of the flow of the second mentioned fluid, and high pressure blast means projecting a stream of fluid at higher pressure across the remainder of the flow of the second mentioned fluid to thereby control heat exchange,

6. In a superheater, a group of spaced tubes conducting steam across a part of the flow of furnace gases, means providing a constantly open bypass at one side of the superheater, and high pressure blast means projecting a flow of fluid at a higher pressure into the bypass, the flow of said fluid being varied in response to the variations of superheat from a predetermined value, the superheat being thereby substantially maintained at predetermined value and being regulated by control of gas flow without the use of dampers.

'7. A method of controlling the flow of gaseous fluid through a conduit, duct or the like, consisting in injecting or projecting across a stream of gaseous fluid flowing therethrough one or more secondary streams of gaseous fluid at higher pressure so as to reduce the effective free area for the flow for the first gaseous fluid through the conduit, duct or the like.

8. A method of controlling the flow of gaseous fluid through a conduit, duct or the like, the method consisting of the steps of injecting or projecting across a primary stream flowing through the conduit one or more secondary streams of gaseous fluid at higher pressure so as to reduce the eifective free area for the flow of the primary stream, the gaseous fluid used for a secondary stream being obtained from the primary stream at a point or points located on the downstream side of the control point and remote therefrom.

9. In apparatus for controlling the flow of gaseous fluid through a conduit, duct or the like, means projecting across a stream of gaseous fluid flowing through the duct one or more secondary streams of gaseous fluid at higher pressure so as to reduce the effective free area for the flow of the first gaseous fluid through the duct, a fan drawing the first gaseous fluid through the duct, and a fan for the higher pressure fluid connected to the discharge of the fan drawing the first gaseous fluid through the conduit, duct or the like, said means including a conduit for the higher pressure fluid, the conduit having an outlet portion the axis of which is transversely related to the direction of flow of lower pressure fluid.

10. In apparatus of the described, a ccntinuing long fluid duct having an inlet and an outlet, means for maintaining a lower pressure at the outlet than at the inlet, and means for varying the rate of flow of a gas through the duct with a given pressure difierential between inlet and outlet; said last-named means including a nozzle in a Wall of the duct with its axis at substantially a right angle to the axis of the duct, the nozzle being supplied with fluid at a pressure substantially higher than that of the fluid normally flowing through the duct.

11. In a water tube steam boiler, a furnace, steam generating tubes heated by the furnace, means connecting said tubes into the boiler circulation, means forming two parallel gas passes jointly receiving the furnace gases beyond said tubes, a superheater in one of said passes while the other pass permits varying proportions of the total amount of furnace gases to bypass the superheater, bypass control means substantially shielded from the furnace gases in the bypass and having substantially all of its parts subject to the furnace gases only after they have passed over gas cooling surfaces beyond said parallel passes, said control means operating without a damper in the bypass to control the flow therethrough and thereby maintain a substantially constant superheat over a wide range of boiler load, said control means also including a blower so connected and arranged as to discharge gases across the bypass.

12. In combination with the steam generating section of a water tube steam boiler, a plurality of gas passes arranged in parallel and jointly receiving furnace gases beyond the steam generating section, a superheater in one of the gas passes while another of said passes permits varying proportions of the furnace gases to bypass the superheater in order that superheat may be controlled and maintained constant While boiler load varies, and means externally of the bypass for controlling the flow of gases through the bypass without the aid of a damper or any equivalent device subject to the heat of the gases in the bypass, said means including a blower and blower discharge connections leading to a wall of the bypass, said last named means being shielded from all high temperature furnace gases.

13. The method of regulating the parallel flow of hot gaseous products of combustion from a furnace through two passages leading to a common chamber having heat absorbing means, consisting of the steps of passing one stream through each passage, subjecting a fluid to the heat of one stream, cooling the gaseous products by the heat absorbing means, withdrawing a portion of the cooled gaseous products, and projecting the withdrawn portion of the gaseous products in a high velocity stream transversely of the flow axis of the other stream to eifect a change in the flow of the uncooled gaseous products through said passages.

14. In heat exchange apparatus, means providing a plurality of passes arranged in parallel, means providing for the flow of a high temperature fluid heat exchange medium through said passes, hollow units disposed in heat exchange relationship to the high temperature medium in one of said passes, heat absorbing means disposed in heat exchange relationship to the heating medium on the downstream side of said passes, and means for conducting the heating medium from a point on the downstream side of said heat absorption means and projecting it in a high velocity stream across the other of said parallel passes to control the movement of gases in heat transfer relationship to said units and thereby control the heating effect thereof.

15. In a Water tube steam boiler, a furnace, steam generating tubes heated by the furnace, means connecting said tubes into the boiler circulation, means forming gas passes arranged in parallel to receive furnace gases and discharge them to a heat transfer zone, a heat exchanger subject to heat of the furnace gases in the first of said passes, heat absorbing means in said zone to cool the gases, and means to inject a portion of the cooled gases in a high velocity stream into the second of said parallel passes to control the flow of furnace gases therethrough.

CHRISTOPHER HUMPHREY DAVY. 

